Magnetic sensor utilizing impedance variation of a soft magnetic element in dependence upon a magnetic field strength and a method of manufacturing the same

ABSTRACT

A magnetic sensor (31) includes an insulator substrate (37) having first and second surfaces opposite to each other, a soft magnetic element having first and second ends opposite to each other and mounted on the first surface of the insulator substrate, and a conductor mounted on the second surface of the insulator substrate, and an output port coupled to the first and the second ends of the soft magnetic element for deriving an impedance of the soft magnetic element between the first and the second ends. The impedance changes in dependence upon a magnetic field strength applied to the soft magnetic element. In the magnetic sensor (31), the soft magnetic element is a soft magnetic wire (33). The conductor is a ground conductor (35) to be grounded. The magnetic sensor may further comprise a short-circuiting conductor (39) connecting the first end of the soft magnetic wire with the ground conductor while the output port is coupled to the short-circuiting conductor and the second end of the soft magnetic wire. The soft magnetic element may comprise a soft magnetic thin film.

BACKGROUND OF THE INVENTION

This invention relates to a magnetic sensor exhibiting variation of animpedance in dependence upon the strength of an external magnetic fieldand, in particular, to a magnetic sensor for use as a magnetic head andthe like.

In recent years, rapid progress has been made in the development ofsmall-sized and high-performance electronic apparatuses. As a readinghead for small-sized and large-capacity hard disks incomputer-associated apparatuses, a conventional magnetic head utilizingelectromagnetic induction is being replaced by a magnetoresistive head(MR head) utilizing a magnetoresistance effect. However, even the MRhead is insufficient to meet further increases in recording density.Under the circumstances, there is a strong demand for a new magneticelement exhibiting wide variation in electric characteristics inresponse to variation in strength of an external magnetic field.

Besides, the MR head is insufficient for use in measurement anddetection of a weak magnetic field, such as measurement of geomagneticstrength or the magnetic field of a brain.

In view of the above, proposal has been made of a magnetic sensor (alsoreferred to as a "magnetic impedance element") comprising a softmagnetic wire to be supplied with a high-frequency current. In responseto the variation in strength of the external magnetic field, the softmagnetic wire exhibits a variation in resistance and inductance, namely,a variation in impedance. Thus, the impedance variation is utilized indetection of magnetic field strength (Japanese Unexamined PatentPublications Nos. 176930/1994 and 248365/1995, Proc. of The Institute ofElectrical Engineers of Japan, Vol. E116, No. 1, page 7 (1996)). Suchmagnetic sensor exhibits wide variation in impedance in response to thevariation in strength of the external magnetic field and therefore has agood performance for a magnetic head.

However, the impedance variation rate (i.e., magnetic field sensitivity)in dependence upon the variation in magnetic field strength is as smallas 10%/Oe.

In order to remove the above-mentioned disadvantage, proposal has beenmade of another magnetic sensor comprising an oscillation circuit formedby a combination of a transistor and a soft magnetic wire. With thisstructure, LC resonance is utilized to improve sensitivity (Journal ofThe Magnetics Society of Japan, Vol. 19, page 469 (1995)). However, thismagnetic sensor not only requires active components but also a pluralityof resistors, capacitors, and diodes. Therefore, the production costinevitably becomes high.

On the other hand, consideration is made about the use of a single layerof an amorphous metal magnetic film in order to realize a small-sizedmagnetic sensor (Proc. of The Institute of Electrical Engineers ofJapan, 115-A, page 949 (1995)). In this magnetic sensor, an electriccurrent is directly supplied to the magnetic film so as to detectimpedance variation in dependence upon the external magnetic field.However, as compared with those metals, such as Cu, Al, and Ag,generally used as a conductor line, the amorphous metal magnetic filmhas a large electrical resistance. Accordingly, efficient excitation cannot be carried out and the impedance variation rate is small.

Furthermore, proposal has been made of a yet another magnetic sensor ormagnetic impedance element comprising a sputtered permalloy film of astripe pattern including a Cu film (Senda et al, The Institute ofElectrical Engineers, Technical Meeting on Magnetics, MAG-95-126, 91(1995)). In addition, proposal has been made of a different magneticsensor comprising CoSiB films with uniaxial magnetic anistropyintroduced and a Cu conductor layer interposed therebetween (Morikawa etal, Journal of The Magnetics Society of Japan, No. 20, page 553 (1996)).These magnetic sensors exhibit an impedance variation rate between -50and +120% with respect to the external magnetic field varying within acertain range. However, magnetic field sensitivity is no more than -5 to+10%/Oe. In addition, it is difficult to control the magneticanisotropy.

In the meanwhile, in the above-mentioned magnetic sensors using softmagnetic elements, the impedance of the magnetic sensor is increased ina frequency band on the order of several ten to several hundredmegahertz (MHz) under the influence of the skin effect and the increasein eddy current loss. This means that the impedance variation inresponse to the variation in strength of the external magnetic field isrelatively small.

In the above-mentioned conventional magnetic sensors, stray capacitanceis produced between the magnetic sensor and other circuit components orconductor lines present around the magnetic sensor. This results inunstable operation of the magnetic sensor.

SUMMARY OF THE INVENTION

It is a first object of this invention to provide a magnetic sensorwhich is hardly disturbed by conductors and dielectrics existing aroundthe magnetic sensor which is therefore stably operable.

It is a second object of this invention to provide a magnetic sensorwhich is high in magnetic field sensitivity, simple in manufacture, andlow in cost.

It is a third object of this invention to provide a magnetic sensorwhich is not only excellent in magnetic field sensitivity but which alsoexhibits wide impedance variation in response to a variation in strengthof an external magnetic field so that stable operation is assured.

It is a fourth object of this invention to provide a magnetic sensorwhich is capable of decreasing a d.c. electric resistance so that ahigher sensitivity is achieved as compared with that comprising amagnetic metal layer or wire to be used also as a conductor metal.

It is a fifth object of this invention to provide a magnetic sensorwhich is capable of suppressing eddy current loss so as to improvemagnetic characteristics in a high-frequency band.

It is a sixth object of this invention to provide a magnetic sensorhaving a large impedance variation rate.

It is a seventh object of this invention to provide a method ofmanufacturing each of magnetic sensors of the types described above.

According to this invention, there is provided a magnetic sensor fordetecting a magnetic field strength, comprising an insulator substratehaving first and second surfaces opposite to each other; a soft magneticelement having first and second ends opposite to each other and mountedon the first surface of the insulator substrate; a conductor mounted onthe second surface of the insulator substrate; and an output portcoupled to the first and the second ends of the soft magnetic elementfor deriving an impedance of the soft magnetic element between the firstand the second ends, the impedance changing in dependence upon amagnetic field strength applied to the soft magnetic element.

According to this invention, there is also provided a magnetic sensorcomprising an insulator substrate and a soft magnetic thin film elementformed on the substrate, which further comprises an inner conductorlayer surrounded by the soft magnetic thin film element through an innerinsulator layer. The soft magnetic thin film element comprises aCo--Nb--Zr thin layer essentially consisting of 80-87 atomic percent Co,10-17 atomic percent Nb, and 1-6 atomic percent Zr.

According to this invention, there is also provided a method ofmanufacturing a magnetic sensor comprising the steps of forming a firstsoft magnetic film on an insulator substrate; forming a first insulatorfilm on the first soft magnetic film; forming a conductor layer on thefirst insulator film; forming a second insulator film to cover theconductor layer except both ends thereof; and forming a second softmagnetic film to cover the second insulator film so as to form a closedmagnetic loop comprising the first and the second soft magnetic films.Each of the first and the second soft magnetic films comprises aCo--Nb--Zr thin film essentially consisting of 80-87 atomic percent Co,10-17 atomic percent Nb, and 1-6 atomic percent Zr.

Herein, description will be made about the reason why theabove-specified composition is selected. In the composition of theCo--Nb--Zr thin film, inclusion of more than 87 atomic percent of Cofavorably increases saturation magnetization but unfavorably increasemagnetostriction which results in deterioration of soft magneticcharacteristics. Therefore, the impedance variation rate in response tothe variation in strength of the external magnetic field is reduced. Inaddition, an amorphous film is difficult to obtain. On the other hand,less than 80 atomic percent of Co decreases saturation magnetization sothat the impedance variation rate in dependence upon the variation instrength of the external magnetic field becomes small.

Zr has a function of transforming the Co--Nb--Zr film into an amorphousfilm and the content of 1 atomic percent or more is required. Thecontent of more than 6 atomic percent is unfavorable becausemagnetostriction is increased to result in deterioration of softmagnetic characteristics.

As regards Nb, the content of 10-16 atomic percent is most preferablebecause zero magnetostriction is achieved. Less than 10 atomic percentincreases positive magnetostriction to cause deterioration of softmagnetic characteristics, i.e., deterioration of the impedance variationrate. On the other hand, more than 16 atomic percent is unfavorablebecause saturation magnetization is degraded.

Thus, since the thin film technique is used in this invention, fineprocess is easy to perform. Like other thin film magnetic sensors, themagnetic sensor of this invention is excellent in this respect ascompared with those using a wire material.

According to this invention, the conductor layer and the magnetic layerare electrically insulated from each other so as to decrease the eddycurrent loss. Therefore, characteristics in high-frequency band areexcellent.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1A and 1B show equivalent circuits of a conventional magneticsensor without any stray capacitance and with stray capacitance,respectively;

FIG. 2 is a perspective view of a magnetic sensor according to a firstembodiment of this invention;

FIG. 3 shows an equivalent circuit of the magnetic sensor of FIG. 2;

FIG. 4 is a perspective view of a magnetic sensor according to a secondembodiment of this invention;

FIG. 5 is a perspective view of a magnetic sensor according to a thirdembodiment of this invention;

FIG. 6 is a perspective view of a magnetic sensor according to a fourthembodiment of this invention as a modification of the magnetic sensor inFIG. 5;

FIG. 7 is a perspective view of a magnetic sensor according to a fifthembodiment of this invention as another modification of the magneticsensor in FIG. 5;

FIG. 8 is a perspective view of a magnetic sensor according to a sixthembodiment of this invention as a modification of the magnetic sensor inFIG. 6;

FIG. 9 is a graph showing the frequency dependency of an impedance withrespect to various values of Lo in the equivalent circuit in FIG. 3;

FIG. 10 is a perspective view of a magnetic sensor according to aseventh embodiment of this invention;

FIG. 11 shows the external magnetic field dependency of an impedance Z,a resistance R, and an inductance L;

FIG. 12 is a perspective view of a magnetic sensor according to aneighth embodiment of this invention;

FIG. 13 is a perspective view of a magnetic sensor according to a ninthembodiment of this invention;

FIG. 14 is a sectional view of the magnetic sensor in FIG. 13;

FIG. 15 is a sectional view of a part of a magnetic sensor according toa tenth embodiment of this invention as a modification of that of FIG.11;

FIG. 16 shows the frequency dependency of the impedance of the magneticsensor of FIG. 10;

FIG. 17 shows the frequency dependency of the impedance Z, theresistance R, and the inductance L of the magnetic sensor of FIG. 13;

FIG. 18 is a perspective view of a magnetic sensor according to atwelfth embodiment of this invention;

FIG. 19 is a cross sectional view of the magnetic sensor illustrated inFIG. 18;

FIG. 20 is a longitudinal sectional view of the magnetic sensorillustrated in FIG. 18;

FIGS. 21A, 21B, 21C, 21D, 21E, and 21F are views for describing amanufacturing process of the magnetic sensor illustrated in FIG. 18;

FIG. 22 shows the external magnetic field dependency of the impedance ofthe magnetic sensor of FIG. 18;

FIG. 23 is a sectional view of the magnetic sensor according to athirteenth embodiment of this invention; and

FIG. 24 shows the external magnetic field dependency of Z, L, and R ofthe magnetic sensor of FIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Prior to description of preferred embodiments of this invention, aconventional magnetic sensor will hereafter be described for a betterunderstanding of this invention.

Referring to FIG. 1A, the conventional magnetic sensor using a softmagnetic element such as wire is represented by an equivalent circuithaving two terminals. The magnetic sensor detects the change in strengthof a magnetic field as the variation in impedance of the soft magneticwire. The impedance is represented by Z=R+jωL (ω being an angularfrequency of an a.c. current supplied to the soft magnetic wire).Specifically, values of the resistance R and the inductance L vary independence upon an external magnetic field. Detailed description will begiven below.

When the soft magnetic wire is supplied with a high-frequency current, amagnetic field is formed to circle the soft magnetic element. When theexternal magnetic field Hex applied to the soft magnetic wire is equalto zero, the soft magnetic wire is excited along an easy magnetizationaxis and a magnetization process by movement of a domain wall is carriedout. Accordingly, when a supply current has a frequency (f) in afrequency band of several megahertz (MHz) or more, relative permeabilityis substantially equal to 1 and the inductance L has a small valuedetermined by a conductor itself. On the other hand, when the externalmagnetic field Hex is applied, magnetization is inclined from anexcitation direction and a magnetization process by rotation ofmagnetization is carried out. Accordingly, the relative permeability ofthe soft magnetic wire is increased and has a maximum value at Hex=Hk(Hk being an anisotropic magnetic field). In addition, at Hex>Hk,magnetization is fixed in a direction of the external magnetic fieldHex, the relative permeability is reduced again. Therefore, theinductance L is changed in dependence upon the strength of the externalmagnetic field Hex and has a maximum value around Hex=Hk.

On the other hand, the resistance R is substantially determined by ad.c. resistance of the conductor when the supply current has a frequencyf in a frequency band of several megahertz (MHz). However, in afrequency band on the order of 10 MHz or more, the resistance R isincreased under the influence of the eddy current loss and the skineffect. The skin effect is determined by a skin depth δ given byEquation (1): ##EQU1## where ρ, f, and μ represents resistivity,frequency, and permeability, respectively. As will be understood fromEquation (1), at such a high frequency f that the skin effect is notnegligible with respect to a film thickness, the skin depth is reducedand the electric resistance is increased when the permeability μ isincreased in dependence upon the external magnetic field Hex. Therefore,in a high frequency range requiring consideration about the skin depthδ, the electric resistance also changes in correspondence to theexternal magnetic field Hex.

In the above-mentioned magnetic sensor, the relative permeability issubstantially equal to 1 in a frequency band on the order of severalmegahertz (MHz). Therefore, the change in inductance L in correspondenceto the external magnetic field is small. However, by utilizing thefeature that the relative permeability has a maximum value when theexternal magnetic field is equal in strength to the anisotropic magneticfield, the variation in impedance in dependence upon the variation instrength of the external magnetic field can be increased.

Thus, the magnetic sensor using the soft magnetic element can detect thevariation in strength of the external magnetic field as the variation inimpedance.

Referring to FIG. 1B, in the conventional magnetic sensor, straycapacitance C is produced between the sensor element and other circuitcomponents and conductor lines therearound. The stray capacitance Cconstitutes a factor of unstable operation.

Now, description will proceed to preferred embodiments of this inventionwith reference to the drawing.

First Embodiment

Referring to FIG. 2, a magnetic sensor 31 according to a firstembodiment of this invention comprises an insulator substrate 37, aconductive soft magnetic wire 33 as a soft magnetic element supported onan upper surface of the insulator substrate 37, a ground conductor film35 formed on a rear surface of the insulator substrate 37, and aconnecting conductor 39 extending from a part of the upper surface ofthe insulator substrate 37 to a part of a side surface thereof toconnect one end of the soft magnetic wire 33 and one end of the groundconductor film 35.

The magnetic sensor 31 is a two-terminal element having two inputterminals (upper right side in the figure) extracted from the softmagnetic wire 33 and the ground condutor film 35, respectively. Thistwo-terminal element has an equivalent circuit illustrated in FIG. 3. InFIG. 3, a capacitance C is produced between the ground conductor film 35and the soft magnetic wire 33. A resistance R, a reactance X, animpedance Z, and a resonant frequency f0 of the equivalent circuit aregiven by Equations (2) through (5): ##EQU2##

In the magnetic sensor having the equivalent circuit in FIG. 3, theimpedance varies in response to the variation in strength of an externalmagnetic field and drastically varies around the resonant frequency f0.Thus, the impedance variation around the resonant frequency f0 isgreater than in a frequency band much lower than the resonant frequencyf0.

In the magnetic sensor according to the first embodiment of thisinvention, the impedance varies in response to application of theexternal magnetic field. As a consequence, the resonant frequency of themagnetic sensor varies also. Therefore, by optimizing the frequency ofthe electric current supplied to the magnetic sensor, the variation inexternal magnetic field can be detected as a very large impedancevariation rate. In other words, magnetic field sensitivity can beincreased.

Furthermore, the first embodiment includes the ground conductor film 35so that occurrence of the stray capacitance in the prior art can besuppressed. In addition, electric field due to the electric currentsupplied to the soft magnetic wire 33 concentrates to an area betweenthe ground conductor film 35 and the connecting conductor 39 throughwhich the electric current flows. Therefore, the magnetic sensor isunsusceptible to disturbance and is therefore stable in operation ascompared with the conventional magnetic sensor which does not have theground conductor film 35. Accordingly, detection of the magnetic fieldcan be stably carried out even when the magnetic sensor is operated in afrequency band lower than the resonant frequency in LC.

An example of the magnetic sensor of the first embodiment is as follows.

By the use of a permalloy wire having a diameter of 50 μm and a lengthof 5 mm as the soft magnetic wire 33 and a polyimide film as theinsulator substrate 37 having a total thickness of 140 μm. The polyimidefilm has 35 μm-thick Cu foils formed on both surfaces thereof. One ofthe Cu foils on the polyimide film was used as the ground conductor film35 while the other Cu foil was partially removed to leave the connectingconductor 39 to be short circuited to the one Cu foil as the groundconductor film 35. Furthermore, one end of the permalloy wire wassoldered to the other Cu foil as the connecting conductor 39.

The magnetic sensor 31 thus obtained was subjected to measurement of theimpedance variation. Specifically, a high-frequency current of 10 MHzwas supplied between the other end of the permalloy wire 33 and theground conductor film 35. The external magnetic field Hex was applied ina longitudinal direction of the permalloy wire 33. In this event, theimpedance variation rate had a maximum value of 38%/Oe at Hex=3 Oe onthe basis of a reference value at Hex=0 Oe.

Second Embodiment

Referring to FIG. 4, a magnetic sensor 41 according to a secondembodiment comprises an insulator film 45 as an insulator substrate, asoft magnetic wire 33 as a soft magnetic element attached to one surfaceof the insulator film 45, a conductor wire 43 as a ground conductorattached to the other surface of the insulator film 45 in parallel tothe soft magnetic wire 33, and a short-circuiting conductor wire 47 as aconnecting conductor connecting one ends of the soft magnetic wire 33with the ground conductor wire 43. The magnetic sensor 41 is atwo-terminal element having two external connection terminals at theother ends of the soft magnetic wire 33 and the ground conductor wire43, respectively.

In the magnetic sensor 41, the soft magnetic wire 33, the groundconductor wire 43, the short-circuiting conductor wire 47, and theinsulator film 45 correspond to the soft magnetic wire 33, the groundconductor film 35, the insulator 37, and the connecting conductor 39 inthe magnetic sensor 31 of FIG. 2, respectively. Therefore, the magneticsensor 41 is also represented by the equivalent circuit in FIG. 3 andits operation is substantially similar to that of the first embodiment.

An example of the magnetic sensor 41 of the second embodiment is asfollows.

A permalloy wire having a diameter of 50 μm and a length of 5 mm as thesoft magnetic wire 33 and a Cu wire having a diameter of 50 μm and alength of 5 mm as the ground conductor wire 43 were adhered to bothsurfaces of a polyimide film having a thickness of 70 μm as theinsulator film 45, respectively. One ends of the permalloy wire and theCu wire were short-circuited by the short-circuiting conductor wire 47to obtain the magnetic sensor 41. The magnetic sensor 41 was thensubjected to measurement of the impedance variation.

Specifically, a high-frequency current of 10 MHz was supplied betweenthe other ends of the permalloy wire 33 and the Cu wire 43. In addition,an external magnetic field Hex was applied in the longitudinal directionof the permalloy wire 33. In this event, the impedance variation ratehad a maximum value of 29%/Oe at Hex=30 Oe.

First Comparative Example

For the purpose of comparison, a permalloy wire having a diameter of 50μm and a length of 5 mm was used alone and a high-frequency current of10 MHz was supplied between both ends of the single permalloy wire.Then, an external magnetic field Hex was applied in the longitudinaldirection of the permalloy wire. In this state, the impedance variationwas detected. As a result, the impedance variation rate at Hex=30 Oe wasno more than 8%/Oe.

Third Embodiment

Referring to FIG. 5, a magnetic sensor 49 according to a thirdembodiment is similar to the magnetic sensor 31 of FIG. 2 except thatthe soft magnetic wire 33 is replaced by a soft magnetic tube 51 with aconductor wire inserted therethrough as a core wire 53. One end of thecore wire 53 is connected to a connecting conductor 39 by soldering orthe like.

As will readily be understood, the magnetic sensor 49 forms atwo-terminal element also represented by the equivalent circuit in FIG.3.

An example of the magnetic sensor 49 of the third embodiment is asfollows.

Through a permalloy tube having an outer diameter of 200 μm as the softmagnetic tube 51, a Cu wire having a diameter of 100 μm as the core wire53 was inserted in a generally coaxial form. A combination of thepermalloy tube and the Cu wire will hereafter be called a coaxial softmagnetic wire for brevity of description. By the use of the coaxial softmagnetic wire and a polyimide film similar to that used in the firstembodiment (i.e., having a total thickness of 140 μm with Cu filmsformed on both surfaces thereof), the magnetic sensor 49 in FIG. 5 wasmanufactured in the manner similar to the first embodiment. The magneticsensor 49 thus obtained was subjected to measurement of the impedancevariation. Specifically, a high-frequency current of 1 MHz was suppliedbetween one ends of the core wire of the coaxial soft magnetic wire anda ground conductor film 35. Furthermore, an external magnetic field Hexwas applied in the longitudinal direction of the permalloy tube. As aresult, the impedance variation rate had a maximum value of 21%/Oe atHex=4 Oe.

Fourth Embodiment

Referring to FIG. 6, a magnetic sensor 55 according to a fourthembodiment of this invention is a modification of the magnetic sensor ofFIG. 5. The ground conductor film 35 and the ground conductor 39 in themagnetic sensor of FIG. 5 are replaced by a ground conductor wire 43 anda short-circuiting conductor wire 47, respectively, and a coaxial softmagnetic wire (51, 53) and the ground conductor wire 43 are attached toboth surfaces of an insulator film 45, respectively, in the mannersimilar to the second embodiment (FIG. 4).

An example of the magnetic sensor 55 of the fourth embodiment isdemonstrated as follows.

By the use of the coaxial soft magnetic wire (51, 53) comprising apermalloy tube (51) having an outer diameter of 200 μm and a Cu wire(53) having a diameter of 100 μm, together with a Cu wire (43) and apolyimide film (45) similar to those used in the second embodiment, themagnetic sensor 55 in FIG. 6 was manufactured. The magnetic sensor 55thus obtained was subjected to measurement of the impedance variation independence upon the strength of an external magnetic field.Specifically, a high-frequency current of 1 MHz was supplied between oneends of the Cu wire 53 of the coaxial soft magnetic wire and the groundconductor wire 43 and the external magnetic field Hex was applied in thelongitudinal direction of the permalloy tube 51. As a result, theimpedance variation rate had a maximum value of 16%/Oe at Hex=4 Oe.

Second Comparative Example

Except that the ground conductor wire 43 was removed, a magnetic sensorsimilar to the magnetic sensor 55 of FIG. 6 was prepared as acomparative example. An electric current of 1 MHz was supplied betweenboth ends of a conductor wire of a coaxial soft magnetic wire of thecomparative example. In this state, the magnetic field dependency of animpedance was measured. As a result, the impedance variation rate had amaximum value as small as 6%/Oe at Hex=4 Oe.

Fifth Embodiment

Referring to FIG. 7, a magnetic sensor 57 according to a fifthembodiment is a modification of the magnetic sensor of FIG. 5.Specifically, the magnetic sensor 57 has an insulator layer 59interposed between a soft magnetic tube 51 and a core wire 53 forming acoaxial soft magnetic wire.

An example of the magnetic sensor 57 of the fifth embodiment isdemonstrated as follows.

A Cu wire having a diameter of 0.5 mm as the core wire 53 was coatedwith a vinyl coating film as the insulator layer 59. Furthermore, theinsulator layer 59 was coated with a permalloy foil having a thicknessof 50 μm as the soft magnetic tube 51 to obtain the coaxial softmagnetic wire. Then, by the use of a polyimide film with Cu foils, themagnetic sensor 57 was manufactured in the manner similar to the firstembodiment. The magnetic sensor 57 thus obtained was subjected tomeasurement of the impedance variation in dependence upon an externalmagnetic field. Specifically, a high-frequency current of 10 MHz wassupplied between one ends of the core wire 53 of the coaxial softmagnetic wire and a ground conductor film 35. Furthermore, the externalmagnetic field Hex was applied in the longitudinal direction of thepermalloy tube. As a result, the impedance variation rate had a maximumvalue of 48%/Oe at Hex=3 Oe.

Sixth Embodiment

Referring to FIG. 8, a magnetic sensor 61 according to a sixthembodiment is a modification of the fourth (FIG. 6) or the fifth (FIG.7) embodiment. Specifically, in the manner similar to FIG. 7, aninsulator layer 59 is interposed between a soft magnetic tube 51 and acore wire 53 forming a coaxial soft magnetic wire in FIG. 6.

An example of the magnetic sensor 61 is demonstrated below.

By the use of a coaxial soft magnetic wire similar to that used in thefifth embodiment together with a Cu wire and a polyimide film similar tothose used in the second embodiment, the magnetic sensor 61 in FIG. 8was manufactured. The magnetic sensor 61 was then subjected tomeasurement of the impedance variation in dependence upon the strengthof an external magnetic field. Specifically, a high-frequency current of10 MHz was supplied between one ends of the core wire 53 of the coaxialsoft magnetic wire and a ground conductor wire 43. Furthermore, theexternal magnetic field Hex was applied in the longitudinal direction ofthe permalloy tube. As a result, the impedance variation rate had amaximum value of 31%/Oe at Hex=3 Oe.

Third Comparative Example

As a third comparative example, the ground conductor wire 43 in themagnetic sensor 61 of FIG. 8 was removed to form a magnetic sensorcomprising a coaxial soft magnetic wire having an insulator layer 59. Anelectric current of 10 MHz was supplied between both ends of themagnetic sensor to measure the magnetic field dependency of animpedance. As a result, the impedance variation rate had a maximum valueas small as 8%/Oe at Hex=3 Oe.

As described above, the magnetic sensor according to each of the firstthrough the sixth embodiments of this invention has the ground conductorso as to have the equivalent circuit illustrated in FIG. 3. In thiscase, the impedance variation in response to the variation in strengthof the external magnetic field can be enlarged further by the use of LCresonance. To demonstrate the above, the value of the inductance L ischanged in the equivalent circuit while the resistance R and thecapacitance C are kept constant at 3Ω and 200 pF, respectively.According to Equations (2) through (4), the impedances Z are calculatedand plotted in FIG. 9.

In the foregoing embodiments, permalloy is selected as a soft magneticmaterial. Instead, most of those metal materials generally used as thesoft magnetic material can be used to achieve the similar effect as faras such material can be formed into a wire, for example, Co--Fe--Si--Bi.

As described above, the magnetic sensor according to each of the firstthrough the sixth embodiments of this invention comprises the softmagnetic wire or the coaxial soft magnetic wire with the conductor coreinserted therethrough, the ground conductor, and the insulatorinterposed therebetween. With this structure, it is possible to suppressoccurrence of the stray capacitance between the soft magnetic elementand surrounding conductors and to achieve stable operation by protectionagainst the disturbance. In addition, by utilizing the capacitanceproduced from addition of the insulator and the conductor, the LCresonance frequency can be freely designed. By utilizing the drasticchange in impedance following the variation of the inductance L independence upon the external magnetic field, the sensitivity can beremarkably improved from several times to several tens of times ascompared with the conventional sensors. In addition, the magnetic sensorof this invention simply comprises the wire material as the softmagnetic element to which the insulator including the conductor layer ora combination of the insulator and the conductor wire is added. Thus,the number of components is reduced and an expensive installation suchas a sputtering apparatus is not required so that the magnetic sensor isobtained at a low cost. Therefore, the magnetic sensor of this inventionis extremely useful for use as a magnetic head and the like.

Seventh Embodiment

Referring to FIG. 10, a magnetic sensor 63 according to a seventhembodiment of this invention comprises a dielectric plate member or aglass substrate 65 as an insulator substrate having upper and lowersurfaces along a predetermined direction, and a linear strip-like softmagnetic thin film 71 as a soft magnetic element having a preselectedwidth and deposited on a part of the upper surface of the glasssubstrate 65 to extend in the predetermined direction. The soft magneticthin film 71 has opposite ends as input and output ends 67 and 69 forsupply of an electric current therebetween. The magnetic sensor 63 isfor detecting, as the impedance variation, the variation in electriccurrent which is caused when the soft magnetic thin film 71 is appliedwith a magnetic field in a direction intersecting the predetermineddirection. In the magnetic sensor 63, the capacitance is intentionallyprovided by depositing a ground conductor film 35 as a conductor on thelower surface of the glass substrate 65.

The soft magnetic thin film 71 forms a two-terminal element having theinput and the output ends 67 and 69. The two-terminal element has anequivalent circuit as illustrated in FIG. 3. In FIG. 3, C represents acapacitance intentionally formed between the ground conductor film 35and the soft magnetic thin film 71. The equivalent circuit has aresistance R, a reactance X, and an impedance Z given by Equations (2)through (4), respectively, and has a resonant frequency given byEquation (5), as described in the foregoing.

In the element having the equivalent circuit in FIG. 3, the impedance ofthe element varies in response to the variation in external magneticfield. It is noted here that the impedance drastically varies around theresonant frequency. Therefore, by monitoring the variation of impedancearound the resonant frequency, wider output variation can be obtained ascompared with monitoring at a low frequency range much lower than theresonant frequency.

The magnetic sensor in this embodiment has the capacitance Cintentionally provided so that the operation is stable as compared withthe conventional magnetic sensors which does not have the groundconductor film 35. Accordingly, detection of the magnetic field can bestably carried out even when the magnetic sensor is operated in afrequency band lower than the resonant frequency in LC resonance of theabove-mentioned conventional magnetic sensor.

Description will be made about a method of manufacturing the magneticsensor 63 in the seventh embodiment (FIG. 10) by the use ofhigh-frequency magnetron sputtering.

At first, the glass substrate 65 having a thickness of 200 μm, a widthof 10 mm, and a length of 20 mm was prepared. Then, the linearstrip-like soft magnetic thin film 71 of Co--Nb--Zr having a thicknessof 4 μm, a width of 4 mm, and a length of 14 mm was deposited on a partof the upper surface of the glass substrate 65 by the sputtering.Subsequently, the ground conductor film 35 of Cu having a thickness of 1μm, a width of 10 mm, and a length of 20 mm was also deposited on thelower surface of the glass substrate 65. The soft magnetic thin film 71was analyzed by EPMA (Electron Probe Microanalysis) to have acomposition of 83.7 at % Co, 2.8 at % Zr, and 13.5 at % Nb.

The magnetic sensor 63 was heated at 400° C. for 2 hours in a vacuum of5.0×10⁻⁵ Torr or less under a rotating magnetic field of H=500 Oe torelax magnetic anisotropy having been introduced during deposition ofthe films. Thereafter, in a vacuum of the same degree under a staticmagnetic field of the same level, heat treatment was carried out tointroduce uniaxial magnetic anisotropy in a widthwise direction of themagnetic sensor 63.

The magnetic sensor 63 as treated was supplied with an electric currentof 40 MHz and was measured for the impedance dependent on variousexternal magnetic field (Hex). The measured data are illustrated in FIG.11. The impedance variation rate was 188%/7.6 Oe and the averagemagnetic field sensitivity was 24.7%/Oe. The maximum magnetic fieldsensitivity was 65.8%/Oe at Hex=7 Oe.

Fourth Comparative Example

As a fourth comparative example, a magnetic sensor was experimentallyprepared which is similar to the magnetic sensor of the seventhembodiment (FIG. 10) except that the ground conductor film 35 is notformed under the glass substrate 65. A process of forming the softmagnetic thin film 71 of Co--Nb--Zr on the upper surface of the glasssubstrate 65 was carried out in the similar manner as the manufacture ofthe example of the magnetic sensor 31 of the seventh embodiment of FIG.10. After forming the soft magnetic thin film 71, heat treatment wasalso carried out in the similar manner. The soft magnetic thin film 71was also analyzed to have a composition of 83.6 at % Co, 2.7 at % Zr,and 13.7 at % Nb. An electric current of 40 MHz was supplied to themagnetic sensor of the fourth comparative example and the externalmagnetic field dependency of the impedance was measured. The impedancevariation rate was 37%/8.6 Oe and the average magnetic field sensitivitywas 4.3%/Oe. The maximum magnetic field sensitivity was 9.5%/Oe atHex=70 Oe.

Eighth Embodiment

Referring to FIG. 12, a magnetic sensor 73 according to an eighthembodiment manufactured by magnetron sputtering is different from thatof the seventh embodiment as will hereafter be described in detail.

The magnetic sensor 73 of the eighth embodiment was manufactured asfollows. A glass substrate 65 having a thickness of 200 μm, a width of10 mm, and a length of 20 mm was prepared. Then, a lower portion of alinear strip-like soft magnetic thin film 71 of Co--Nb--Zr having athickness of 4 μm, a width of 4 mm, and a length of 14 mm was depositedon a part of the upper surface of the glass substrate 65. Subsequently,a Cu film 75 having a thickness of 1 μm, a width of 2 mm, and a lengthof 20 mm was formed on a center line of the lower portion of the softmagnetic thin film 71. Thereafter, on the lower portion of the softmagnetic thin film 71 over the upper surface of the Cu film 75, an upperportion of the soft magnetic thin film 71 of Co--Nb--Zr was deposited tohave a maximum thickness of 4 μm, a width of 4 mm, and a length of 14mm. Finally, on the lower surface of the glass substrate 65, a groundconductor film 35 of Cu was deposited which has a thickness of 1 μm, awidth of 10 mm, and a length of 20 mm.

The soft magnetic thin film 71 was also analyzed to have a compositionof 83.4 at % Co, 3.0 at % Zr, and 13.6 at % Nb.

In the manner similar to the seventh embodiment, uniaxial magneticanisotropy was introduced into the magnetic thin film 71 in a widthwisedirection thereof. Subsequently, the magnetic sensor 73 was suppliedwith an electric current of 80 MHz and the impedance variation rate wasmeasured by application of the external magnetic field varied. Theimpedance variation rate was 85%/8.1 Oe and the average magnetic fieldsensitivity was 10.7%/Oe. The maximum magnetic field sensitivity was25.1%/Oe at Hex=7 Oe.

Fifth Comparative Example

A magnetic sensor of a fifth comparative example was experimentallyprepared which is similar to the magnetic sensor 73 of the eighthembodiment (FIG. 12) except that the ground conductor film 35 was notformed on the lower surface of the glass substrate 65. Thus, themagnetic sensor of the fifth comparative example comprises the softmagnetic thin film 71 of Co--Nb--Zr and the Cu film 75 formed on theupper surface of the glass substrate 65.

Under the condition similar to the eighth embodiment, heat treatment wascarried out to introduce magnetic anisotropy. Thereafter, an electriccurrent of 80 MHz was supplied. In this state, the external magneticfield (Hex) dependency of the impedance was measured. As a result, theimpedance variation rate was 50%/9 Oe and the average magnetic fieldsensitivity was about 6%/Oe. The maximum magnetic field sensitivity was12.3%/Oe at Hex=7 Oe.

Ninth Embodiment

Referring to FIGS. 13 and 14, a magnetic sensor 77 according to a ninthembodiment was manufactured by magnetron sputtering in the manner whichwill presently be described. At first, a glass substrate 65 having athickness of 200 μm, a width of 10 mm, and a length of 20 mm wasprepared. Then, a first linear strip-like soft magnetic thin film 79 ofCo--Nb--Zr having a thickness of 4 μm, a width of 4 mm, and a length of14 mm was deposited on a part of the upper surface of the glasssubstrate 65. Thereafter, on the first soft magnetic thin film 79, afirst SiO₂ film 81 having a thickness of 0.5 μm, a width of 3 mm, and alength of 18 mm was formed. Subsequently, a Cu film 75 having athickness of 1 μm, a width of 2 mm, and a length of 20 mm was depositedon the first SiO₂ film 81. Furthermore, on the first SiO₂ film 81 andthe Cu film 75, a second SiO₂ film 83 having a thickness of 0.5 μm, awidth of 3 mm, and a length of 18 mm was formed. Furthermore, on thefirst soft magnetic thin film 79 and the second SiO₂ film 83, a secondlinear strip-like soft magnetic thin film 85 having a thickness of 4 μm,a width of 4 mm, and a length of 14 mm was formed. Finally, a groundconductor film 35 of Cu having a thickness of 1 μm, a width of 10 mm,and a length of 20 mm was deposited on the lower surface of the glasssubstrate 65.

Each of the first and the second soft magnetic thin films 79 and 85 hada composition of 84.1 at % Co, 2.7 a % Zr, and 13.2 at % Nb as analyzedby EPMA.

In the manner similar to the seventh embodiment, uniaxial magneticanisotropy was introduced into the magnetic thin films 79 and 85 in awidthwise direction thereof. Then, the magnetic sensor 77 was suppliedwith an electric current of 120 MHz and the impedance was measured asthe external magnetic field Hex of various strengths is applied. As aresult, the impedance variation rate was 35%/8.0 Oe and the averagemagnetic field sensitivity was 43.8%/Oe. At Hex=7 Oe, a curverepresentative of the impedance variation with respect to the externalmagnetic field Hex exhibited the maximum gradient with the maximumimpedance variation rate of 205%/Oe.

Sixth Comparative Example

A magnetic sensor of a sixth comparative example was experimentallyprepared which is similar to the magnetic sensor 77 of the ninthembodiment (FIGS. 13 and 14) except that the ground conductor film 35was not formed on the lower surface of the glass substrate 65.

Under the condition similar to the ninth embodiment, heat treatment wascarried out to introduce magnetic anisotropy. Thereafter, an electriccurrent of 120 MHz was supplied. In this state, the external magneticfield dependency of the impedance was measured. As a result, theimpedance variation rate was 120%/8.2 Oe and the average magnetic fieldsensitivity was about 14.6%/Oe. The maximum magnetic field sensitivitywas 23%/Oe at Hex=7 Oe.

Tenth Embodiment

Referring to FIG. 15, a magnetic sensor 95 according to a tenthembodiment has a structure similar to the magnetic sensor 77 of theninth embodiment (FIGS. 15 and 16) except that the first and the secondsoft magnetic thin films 79 and 85 are replaced by first and second softmagnetic layers 87 and 91 each of which has a stacked structure.

The magnetic sensor 95 was manufactured in the following manner. Atfirst, a glass substrate 65 having a thickness of 200 μm, a width of 10mm, and a length of 20 mm was prepared. Then, on a part of the uppersurface of the glass substrate 65, a soft magetic thin film 87a ofCo--Nb--Zr having a thickness of 1 μm, a width of 4 mm, and a length of14 mm was deposited. Subsequently, on the soft magnetic thin film 87a,an AlN film 89a having a thickness of 0.1 μm, a width of 4 mm, and alength of 18 mm was formed. Likewise, similar soft magnetic thin films87b through 87d and similar AlN films 89b and 89c were alternatelydeposited to form the first soft magnetic layer 87 of a stackedstructure with three AlN films interposed. Thereafter, on the first softmagnetic layer 87, specifically, on a part of the upper surface of thetopmost soft magnetic thin film 87d, an AlN film 81 having a thicknessof 0.5 μm, a width of 3 mm, and a length of 18 mm was deposited.Subsequently, a Cu film 75 having a thickness of 1 μm, a width of 2 mm,and a length of 20 mm was formed on the AlN film 81 except both endsthereof. Then, on the AlN film 81 and the Cu film 75, an AlN film 83having a thickness of 0.5 μm, a width of 3 mm, and a length of 18 mm wasformed. Then, on the AlN film 83 and on the first soft magnetic layer87, namely, on the uppermost soft magnetic thin film 87d, another set ofsoft magnetic thin films 91a through 91d of Co--Nb--Zr and three AlNfilms 93a through 93c are alternately deposited to form the second softmagnetic layer 91 with the three AlN films interposed. Finally, a groundconductor film 35 of Cu having a thickness of 1 μm, a width of 10 mm,and a lengthof 20 mm was deposited on the lower surface of the glasssubstrate 65. Each of the soft magnetic thin films 87a through 87d and91a through 91d had a composition of 83.5 at % Co, 3.1 at % Zr, and 13.4at % Nb.

In the manner similar to the seventh embodiment, uniaxial magneticanisotropy was introduced into the soft magnetic layers in a widthwisedirections thereof. Then, the magnetic sensor 95 was supplied with anelectric current of 120 MHz and the impedance was measured in theexternal magnetic field (Hex) with the strength variously changed. As aresult, the impedance variation rate was 212%/8.0 Oe and the averagemagnetic field sensitivity was 26.5%/Oe. The maximum magneticsensitivity was 128%/Oe at Hex=7 Oe.

Seventh Comparative Example

A magnetic sensor of a seventh comparative example was experimentallyprepared which is similar to the magnetic sensor 77 of the ninthembodiment (FIG. 15) except that the ground conductor film 35 is notformed on the lower surface of the glass substrate 65. Heat treatmentwas carried out in the condition similar to that of the ninth embodimentto introduce magnetic anisotropy. Thereafter, an electric current of 120MHz was supplied. In this state, the external magnetic field dependencyof the impedance was measured. As a result, the impedance variation ratewas 83%/8.5 Oe and the average magnetic field sensitivity was about9.8%/Oe. The maximum magnetic field sensitivity was 22.5%/Oe at Hex=7Oe.

Eleventh Embodiment

A magnetic sensor according to an eleventh embodiment is similar to themagnetic sensor 77 of the ninth embodiment (FIGS. 13 and 14) except thatthe soft magnetic thin films 81 and 83 of Co--Nb--Zr are replaced bypermalloy of 4 μm thickness.

The magnetic sensor was heated at 500° C. for 2 hours in a vacuum of5.0×10⁻⁶ Torr or less under a static magnetic field of H=500 Oe tointroduce uniaxial magnetic anisotropy in a widthwise direction thereof.Thereafter, the magnetic sensor was supplied with an electric current of40 MHz, and the external magnetic field (Hex) dependency of animpedance, an inductance, and a resistance was measured. The impedancevariation rate was 72%/40 Oe and the average magnetic field sensitivitywas 18.0%/Oe. The maximum magnetic field sensitivity was 43%/Oe atHex=2.5 Oe.

Eighth Comparative Example

A magnetic sensor of an eighth comparative example was experimentallymanufactured which is similar to the magnetic sensor in the eleventhembodiment except that the ground conductor film (35 in FIGS. 13 and 14)is omitted. Like in the eleventh embodiment, an electric current of 40MHz was supplied. In this state, the magnetic field dependency of theimpedance was measured. As a result, the impedance variation rate was35%/4.1 Oe and the average magnetic field sensitivity was about 8.5%/Oe.The maximum magnetic field sensitivity was 16%/Oe at Hex=2.5 Oe.

According to each of the seventh through the eleventh embodiments ofthis inventions described above, in the magnetic sensor using the softmagnetic thin film to detect, as impedance variation, variation instrength of the external magnetic field, the ground conductor film(ground electrode) is formed so as to intentionally provide thecapacitance. Therefore, the magnetic sensor is advantageous in that theoperation is stable and that the drastic change in impedanceaccompanying LC resonance in the equivalent circuit in FIG. 3 can beutilized. Thus, the disadvantages in the above-mentioned conventionalsensors can be readily removed.

The value of the capacitance C in the equivalent circuit in FIG. 3 canbe selected to a specific value in a design stage. The resistance R₀ andthe inductance L₀ illustrated in the figure vary in dependence upon theexternal magnetic field.

Specifically, in the equivalent circuit having the impedance given byEquations (2) through (4), the inductance L is variously changed withthe resistance R and the capacitance C kept constant at 3Ω and 200 pF,respectively. In this state, the impedance is calculated as plotted inFIG. 16. As already described, in the magnetic sensor of each of theseventh through the eleventh embodiments of this invention, thepermeability of the soft magnetic films is varied under the influence ofthe external magnetic field. Therefore, the variation of the inductanceL shown in FIG. 16 is actually caused by the external magnetic field.For example, it is assumed that, when an electric current of 70 MHz issupplied, the permeability is increased by application of the externalmagnetic field and the inductance L varies from 20nH to 5 nH. In thisevent, the impedance varies from 12Ω to 80Ω, exhibiting the variationrate of 600% or more. Practically, since the electric resistance isvaried under the influence of the skin effect, the situation is not sosimple.

FIG. 17 shows the frequency dependency of the impedance measured in theninth embodiment, which has a tendency substantially identical with thatillustrated in FIG. 16. Thus, it will be noted that the impedancevariation following application of the magnetic field to the magneticsensor causes the variation of the resonant frequency of the magneticsensor. Therefore, by optimizing the frequency of the electric currentsupplied, the variation in strength of the external magnetic field canbe detected as a very large impedance variation rate.

In the ninth and the tenth embodiments, the soft magnetic thin film isformed by amorphous Co--Nb--Zr. In the eleventh embodiment, permalloy isused. However, any material excellent in soft magnetic effect can beused instead. In place of the Cu film, any material selected fromlow-resistance electrode metals such as Al, Ag, and Au can be used. Theinsulator film may be formed by various compounds excellent ininsulation, such as Al₂ O₃ and Si₃ O₄, instead of SiO₂ and AlN.

Now, description will be made as regards a magnetic sensor having thesoft magnetic element comprising a Co--Nb--Zr film similar to the ninthand the tenth embodiments shown in FIGS. 13, 14, and 15 but having noground conductor film as have been described as the sixth and theseventh comparative examples. It should be noted that the magneticsensor without the ground conductor film is provided with an improvedmagnetic field sensitivity above 15%/Oe by the use of the Co--Nb--Zrfilm of a specific composition essentially consisting of 80-87 at % Co,10-17 at % Nb, and 1-6 at % Zr.

Twelfth Embodiment

This embodiment is similar to the ninth embodiment of FIGS. 13 and 14but without the ground conductor film 35 as in the sixth comparativeexample.

Referring to FIGS. 18 through 20, a magnetic sensor 85 according to atwelfth embodiment of this invention comprises a glass substrate 65 asan insulator substrate, and a soft magnetic element formed on the glassplate 65. The magnetic element is a clad type structure and comprises,as an outer clad layer of the soft magnetic element, a soft magneticlayer 99 comprising a Co--Nb--Zr film having a thickness of 1μm, a Cufilm 75 as a core conductor of the soft magnetic element, having athickness of 1 μm and formed at a center portion, an insulator layer 101comprising 0.5 μm-thick SiO₂ films 81 and 83 interposed between the softmagnetic layer 99 and the conductor layer 75.

The soft magnetic layer 99 comprises a first soft magnetic thin film 79formed on the glass substrate 65, and a second soft magnetic thin film85 formed on and above the first soft magnetic thin film 79. Theinsulator layer 101 comprises the SiO₂ films 81 and 83 as first andsecond insulator films. The first insulator film 81 is interposedbetween the Cu film 75 and the first soft magnetic thin film 79 whilethe second insulator film 83 is interposed between the Cu film 75 andthe second soft magnetic thin film 85. The first and the secondinsulator films 81 and 83 are kept in tight contact with each other atopposite peripheral portions thereof.

The magnetic sensor 97 of the twelfth embodiment was manufactured asfollows to obtain samples 1 through 10. In addition, comparative samples11 through 15 were obtained as a ninth comparative example.

Referring to FIGS. 21A through 21F, the magnetic sensor 97 having thestructure illustrated in FIGS. 18 through 20 was manufactured on theglass substrate 65 having a thickness of 1 mm. By the use of Co--Nb--Zralloy targets of a several kinds of compositions, an Nb pellet, and a Zrpellet, Co--Nb--Zr films of different compositions were formed. Thecompositions of the Co--Nb--Zr films deposited were analyzed by EPMA.

At first referring to FIG. 21A, a mask was formed on the glass substrate65 having a dimension of 10 mm×20 mm. As illustrated in FIG. 21B, thefirst soft magnetic thin film 79 of Co--Nb--Zr having a width of 4 mm, alength of 14 mm, and a thickness of 1 μm was formed by sputtering. Nextreferring to FIG. 21C, the first insulator film 81 of SiO₂ having awidth of 3 mm, a length of 16 mm, and a thickness of 0.5 μm was formedby RF magnetron sputtering by the use of a mask. Next referring to FIG.21D, on the first insulator film 81, the Cu film 75 having a width of 2mm, a length of 20 mm, and a thickness of 1 μm was formed to extend inthe longitudinal direction beyond the both ends of the first insulatorfilm 81. Then, as ilustrated in FIG. 21E, the second insulator film 83of SiO₂ having a width of 3 mm, a length of 16mm, and a thickness of 0.5μm was formed to cover the center portion of the Cu film 75 and tooverlap the first insulator film 81. Thereafter, as illustrated in FIG.21F, the second soft magnetic thin film 85 of Co--Nb--Zr having a widthof 4 mm, a length of 14 mm, and a thickness of 1 μm was formed to coverthe second insualtor film 83. Thus, the magnetic sensor 97 was obtained.The magnetic sensor 97 experimentally manufactured had a dimension suchthat the Co--Nb--Zr film had a length of 14 mm and a width of 4 mm andthat the Cu film (Cu electrode) had a length of 20 mm and a width of 2mm. The magnetic sensor 97 was subjected to heat treatment at 400° C.for 2 hours in a vacuum of 5.0×10⁻⁶ Torr or less and under a rotatingmagnetic field of H=500 Oe to relax magnetic anisotropy having beenintroduced during deposition of the films. Thereafter, heat treatmentwas carried out in a vacuum of the same degree and a static magneticfield of the same level to introduce uniaxial magnetic anisotropy in awidthwise direction of the magnetic sensor 97.

Then, with opposite ends of the Cu film 75 of the magnetic sensor 97used as input terminals, an electric current of 10 MHz was supplied. Inthis state, the external magnetic field dependency of the impedance wasmeasured. The impedance variation rate and the result of analysis of thecomposition by EPMA are shown in Table 1. For Sample 1 in Table 1, theexternal magnetic field dependency is plotted in FIG. 22. In Table 1,Samples 1 through 10 use the compositions of Co--Nb--Zr film of thisinvention while Samples 11 through 15 according to the ninth comparativeexample use other compositions different from this invention.

                  TABLE 1                                                         ______________________________________                                                                        Magnetic                                             Composition   Impedance  Field Sen-                                    Sample   Co      Nb      Zr    Variation                                                                              sitivity                              No.      (at %)  (at %)  (at %)                                                                              Rate     (%/Oe)                                ______________________________________                                        Twelfth                                                                             1      84.3    12.6  3.1   107 %/6.5 Oe                                                                           16.5                                Embo- 2      83.8    13.5  2.8   103 %/6.2 Oe                                                                           16.6                                diment                                                                              3      83.2    13.5  3.3   100 %/6.0 Oe                                                                           16.7                                      4      86.5    10.5  3.0   130 %/8.2 Oe                                                                           15.9                                      5      80.3    13.6  6.1    95 %/5.9 Oe                                                                           16.1                                      6      84.1    13.9  2.0   115 %/7.5 Oe                                                                           15.3                                      7      85.5    12.2  2.3   126 %/8.2 Oe                                                                           15.4                                      8      84.5    13.7  1.8   145 %/8.8 Oe                                                                           16.5                                      9      83.2    11.5  5.3   109 %/6.6 Oe                                                                           16.5                                      10     82.2    16.3  1.5    99 %/6.2 Oe                                                                           16.0                                Ninth 11     88.6    10.9  0.5   143 %/18 Oe                                                                             7.9                                Compa-                                                                              12     84.2     9.0  6.8   135 %/15 Oe                                                                             9.0                                rative                                                                              13     80.2    18.5  1.3    56 %/8.9 Oe                                                                            6.3                                Ex-   14     79.2    15.6  5.2    80 %/8 Oe                                                                             10.0                                ample 15     87.2     9.2  3.8   138 %/16 Oe                                                                             8.6                                ______________________________________                                    

It is noted from Table 1, Samples 1-10 has a magnetic field sensitivityabove 15%/Oe comparing with Comparative Examples 11-15.

Tenth Comparative Example

As a magnetic sensor of a tenth comparative example, a Co--Nb--Zr filmhaving a thickness of 2 μm, a length of 4 mm, and a thickness of 4 mmwas formed alone on the glass substrate 65 having a thickness of 1 mm inthe twelfth embodiment. In the manner similar to the twelfth embodiment,the heat treatment was carried out within a magnetic field. The softmagnetic element was directly supplied with an electric current of 10MHz. In this state, the external magnetic field dependency of theimpedance was measured. As a result, the impedance variation rate was30%/7 Oe and the magnetic field sensitivity was 4.3%/Oe. The film had acomposition of 83.8 at % Co, 13.3 at % Nb, and 2.9 at % Zr. As comparedwith Sample 2 in the twelfth embodiment, the magnetic sensor of thetwelfth embodiment (FIG. 20) having the core conductor 75 in addition tothe soft magnetic layer 99 is obviously superior.

Eleventh Comparative Example

As an eleventh comparative example, a magnetic sensor was prepared whichis similar to the magnetic sensor of the twelfth embodiment (FIGS. 18through 20) except that the insulator layer 101 comprising the SiO₂ filmis removed. Thus, the soft magnetic element comprises the glasssubstrate 65, the Cu film 75, and the Co--Nb--Zr film as the softmagnetic layer 99. In the manner similar to the twelfth embodiment,magnetic heat treatment was carried out. In the manner similar to thetwelfth embodiment, the soft magnetic element is supplied with anelectric current of 10 MHz. In this state, the external magnetic fielddependency of the impedance was measured. As a result, the impedancevariation rate was 50%/7 Oe and the magnetic field sensitivity was6%/Oe. The Co--Nb--Zr film had a composition of 83.3 at % Co, 13.8 at %Nb, and 2.9 at % Zr. As compared with Sample 3 in the twelfthembodiment, the magnetic sensor of the twelfth embodiment (FIGS. 18through 20) having the insulator layer between the soft magnetic layerand the conductor layer is obviously superior.

Twelfth Comparative Example

As a twelfth comparative example, a magnetic sensor similar to themagnetic sensor 97 of the twelfth embodiment (FIGS. 18 through 20)except that the soft magnetic layer 99 is formed by permalloy instead ofCo--Nb--Zr was prepared. The magnetic sensor was evaluated for magneticimpedance characteristics. In the manner similar to the twelfthembodiment, an electric current of 10 MHz was supplied. In this state,the external magnetic field dependency of the impedance was measured. Asa result, the impedance variation rate was 45%/9 Oe and the magneticfield sensitivity was 5%/Oe.

Thirteenth Embodiment

This embodiment is similar to the tenth embodiment of FIG. 15 butwithout the ground conductor film 35 as in the sixth comparativeexample.

Referring to FIG. 23, a magnetic sensor 109 according to a thirteenthembodiment is similar to that of the twelfth embodiment (FIGS. 18through 20) except that the first and the second soft magnetic thinfilms 79 and 85 each of which comprises a single layer of the Co--Nb--Zrfilm are replaced by first and second soft magnetic layers 103 and 107each of which has a stacked structure.

As illustrated in FIG. 23, the first soft magnetic layer 103 comprisesfour soft magnetic thin films 87a through 87d of Co--Nb--Zr each havinga thickness of 0.25 μm with three insulator films 89a through 89c eachhaving a thickness of 0.1 μm interposed. Likewise, the second softmagnetic layer 107 comprises four soft magnetic thin films 91a through91d of Co--Nb--Zr each having a thickness of 0.25 μm with threeinsulator films 93a through 93c each having a thickness of 0.1 μminterposed. A combination of the first and the second soft magneticlayers 103 and 107 forms the magnetic sensor or magnetic impedanceelement 109.

In the manner similar to the twelfth embodiment, magnetic heat treatmentwas carried out. An electric current of 40 MHz was supplied to the Cufilm 75. In this state, the external magnetic field dependency of eachof an impedance, an inductance, and an resistance was measured. As aresult, the impedance, the inductance, and the resistance exhibit thevariation as illustrated in FIG. 24. In this case, the impedancevariation rate was 12%/8 Oe and the magnetic field sensitivity was15%/Oe. Each of the soft magnetic thin film had a composition of 84 at %Co, 12.8 at % Nb, and 3.2 at % Zr. As compared with a thirteenthcomparative example which will be described in the following, thismagnetic sensor is excellent in characteritics in a high frequencyrange.

Thirteenth Comparative Example

The magnetic sensor of Comparative Sample 11 in Table 1 was suppliedwith an electric current of 40 MHz, in the manner similar to thethirteenth embodiment. In this state, the external magnetic fielddependency of the impedance was measured. As a result, the impedancevariation rate was 80%/8 Oe and the magnetic field sensitivity was10%/Oe.

Fourteenth Embodiment

A magnetic sensor according to a fourteenth embodiment is similar to themagnetic sensor 97 in the twelfth embodiment (FIGS. 18 through 20)except that Si₃ N₄ films were used as the insulator layer 101 instead ofSiO₂. In the manner similar to the twelfth embodiment, magnetic heattreatment was carried out. In the state where an electric current of 10MHz was supplied, the impedance variation rate was measured at variousstrengths of the external magnetic field. As a result, the impedancevariation rate was 110%/6.5 Oe and the magnetic field sensitivity was16.9%/Oe.

Fifteenth Embodiment

A magnetic sensor according to a fifteenth embodiment is similar to themagnetic sensor 97 in the twelfth embodiment (FIGS. 18 through 29)except that Al₂ O₃ films were used as the insulator layer 101 instead ofSiO₂. In the manner similar to the twelfth embodiment, magnetic heattreatment was carried out. In the state where an electric current of 10MHz was supplied, the impedance variation rate was measured at variousstrengths of the external magnetic field. As a result, the impedancevariation rate was 113%/6.7 Oe and the magnetic field sensitivity was16.9%/Oe.

Sixteenth Embodiment

A magnetic sensor according to a sixteenth embodiment is similar to themagnetic sensor 97 in the twelfth embodiment (FIGS. 18 through 20)except that the insulator layer 101 of SiO₂ is replaced by AlN films. Inthe manner similar to the twelfth embodiment, magnetic heat treatmentwas carried out. In the state where an electric current of 10 MHz wassupplied, the impedance variation rate was measured at various strengthsof the external magnetic field. As a result, the impedance variationrate was 103%/6.3 Oe and the magnetic field sensitivity was 16.3%/Oe.

As described above, according to each of the twelfth through thesixteenth embodiments of this invention, the magnetic thin film ofCo--Nb--Zr amorphous metal including the conductor metal layer is usedas the soft magnetic element in the magnetic sensor. With thisstructure, as compared with the conventional sensor which uses themagnetic metal layer or the magnetic metal wire also as the conductormetal, the d.c. electric resistance is reduced so that a highersensitivity is achieved.

In addition, in each of the twelfth through the sixteenth embodiments ofthis invention, the glass ceramic insulator layer is interposed betweenthe conductor metal layer and the Co--Nb--Zr amorphous metal magneticthin film. Therefore, the d.c. current for application of the externalmagnetic field does not flow through the amorphous metal magnetic thinfilm. It is therefore possible to reduce the eddy current loss and toimprove the magnetic characteristics in a high frequency band ascompared with the structure having no insulator layer.

In the twelfth through the sixteenth embodiments of this invention, theCo--Nb--Zr layer does not have a single-layer structure but has astacked structure with the glass ceramic layers interposed. It istherefore possible to cope with a still higher frequency band.

In the twelfth through the sixteenth embodiments of this invention, byselecting the appropriate composition of the amorphous Co--Nb--Zrmagnetic metal layer, the magnetic sensor achieves the impedancevariation rate greater than that obtained by the conventional sensorsusing the permalloy thin film or the Co--Si--B thin film.

What is claimed is:
 1. A magnetic sensor for detecting a magnetic field strength, comprising:an insulator substrate having first and second surfaces opposite to each other; a soft magnetic element having first and second ends opposite to each other and mounted on said first surface of said insulator substrate; and a ground conductor mounted on said second surface of said insulator substrate; wherein said ground conductor comprises a conductor film formed on said second surface of said insulator and is conductively coupled to said first end of said soft magnetic element, and wherein an impedance of said soft magnetic element between said first and said second ends thereof changes in dependence upon a magnetic field strength applied to said soft magnetic element.
 2. A magnetic sensor for detecting a magnetic field strength, comprising:an insulator substrate having first and second surfaces opposite to each other; a soft magnetic wire having first and second ends opposite to each other and mounted on said first surface of said insulator substrate; and a ground conductor mounted on said second surface of said insulator substrate; wherein a short circuiting conductor connects said first end of said soft magnetic wire with said ground conductor; and wherein an impedance of said soft magnetic wire between said first and said second ends thereof changes in dependence upon a magnetic field strength applied to said soft magnetic wire.
 3. A magnetic sensor for detecting a magnetic field strength, comprising:an insulator substrate having first and second surfaces opposite to each other; a soft magnetic wire having first and second ends opposite to each other and mounted on said first surface of said insulator substrate; and a ground conductor mounted on said second surface of said insulator substrate; wherein a short circuiting conductor connects said first end of said soft magnetic wire with said ground conductor; wherein an impedance of said soft magnetic wire between said first and said second ends thereof changes in dependence upon a magnetic field strength applied to said soft magnetic wire; and wherein said soft magnetic wire comprises a coaxial soft magnetic wire having an outer soft magnetic portion and an inner conductor wire enclosed therein, said inner conductor wire being connected to said ground conductor.
 4. A magnetic sensor as claimed in claim 3, wherein said soft magnetic element further comprises an insulator layer interposed between said outer soft magnetic portion and said internal conductor wire of said coaxial soft magnetic wire.
 5. A magnetic sensor for detecting a magnetic field strength, comprising:an insulator substrate having first and second surfaces opposite to each other; a soft magnetic wire having first and second ends opposite to each other and mounted on said first surface of said insulator substrate; and a ground conductor mounted on said second surface of said insulator substrate; wherein a short circuiting conductor connects said first end of said soft magnetic wire with said ground conductor; wherein an impedance of said soft magnetic wire between said first and said second ends thereof changes in dependence upon a magnetic field strength applied to said soft magnetic wire; and wherein said ground conductor comprises a conductor wire attached to said second surface of said insulator substrate.
 6. A magnetic sensor as claimed in claim 1, wherein said soft magnetic element comprises a soft magnetic thin film.
 7. A magnetic sensor as claimed in claim 6, wherein said ground conductor comprises Cu, Ag, Au, Al, or an alloy containing at least one of Cu, Ag, Au, and Al.
 8. A magnetic sensor for detecting a magnetic field strength, comprising:an insulator substrate having first and second surfaces opposite to each other; a soft magnetic element having first and second ends opposite to each other and mounted on said first surface of said insulator substrate; and a ground conductor mounted on said second surface of said insulator substrate; wherein said ground conductor comprises a conductor film formed on said second surface of said insulator and is conductively coupled to said first end of said soft magnetic element; wherein an impedance of said soft magnetic element between said first and said second ends thereof changes in dependence upon a magnetic field strength applied to said soft magnetic element; and wherein said soft magnetic element comprises an inner conductor layer extending in a longitudinal direction of said soft magnetic element, an insulator layer surrounding an outer periphery of said inner conductor layer, and a soft magnetic thin film covering said insulator layer, said inner conductor layer comprising Cu, Ag, Au, Al, or an alloy containing at least one of Cu, Ag, Au, and Al, and said insulator layer comprising at least one of SiO₂, Si₃ N₄, and AlN.
 9. A magnetic sensor for detecting a magnetic field strength, comprising:an insulator substrate having first and second surfaces opposite to each other; a soft magnetic element having first and second ends opposite to each other and mounted on said first surface of said insulator substrate; and a ground conductor mounted on said second surface of said insulator substrate; wherein said ground conductor comprises a conductor film formed on said second surface of said insulator and is conductively coupled to said first end of said soft magnetic element; wherein an impedance of said soft magnetic element between said first and said second ends thereof changes in dependence upon a magnetic field strength applied to said soft magnetic element; and wherein said soft magnetic element comprises an inner conductor layer and a stacked structure around said inner conductor layer, said stacked structure comprising a plurality of soft magnetic thin films stacked with insulator layers interposed therebetween, said inner conductor layer being made of at least one of Cu, Ag, Au, Al or alloys thereof, and each of said insulator layers being made of at least one of SiO₂, Si₃ N₄, and AlN. 